The two-reflector system invented by Nicholas Cassegrain has been used extensively in optical telescopes, primarily to achieve a long effective focal length with a convenient physical configuration. During the late 1950s, widespread interest developed in the use of this type of system for microwave frequencies.

Axially symmetrical dual-reflector antennas (Cassegrain) classical or shaped) are of interest in radio astronomy and in Earth-station antenna technology. The design of such systems is often restricted by some mechanical constraints, the type of feed horn used, and the budget of the project (closely related to the size of the reflectors). Taking into account all of the above, various sets of input parameters, representing various solutions, are considered. From these input parameters, the overall geometry of the antenna is derived in closed form.

•What is a Cassegrain antenna?In telecommunication and radar use, a Cassegrain antenna is an antenna in which the feed radiator is mounted at or near the surface of a concave main reflector and is aimed at a convex subreflector. Both reflectors have a common focal point. Energy from the feed unit (a feed horn mostly) illuminates the secondary reflector, which reflects it back to the main reflector, which then forms the desired forward beam.

Cassegrain antenna is a double reflector system which has many interesting features such as high efficiency, low noise temperature performance, and easy accessibility to electronic equipment. 01

Photo: Cassegrain antenna

02 Geometry:

The classical Cassegrain geometry, shown in the below fig, employs a parabolic contour for the main dish and a hyperbolic contour for the sub dish. One of the two foci of the hyperbola is the real focal point of the system, and is located at the center of the feed; the other is a virtual feed point which is the real focal point of the system, and is located at the center of the feed; the other is a virtual focal point which is located at the focus of the parabola. As a result, all parts reflected from both surfaces, travel equal distances to a plane in front of the antenna.
Fig: Geometry of Cassegrain Antenna
Geometrical parameters for selected Cassegrain antenna
Type...

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said.ghnimi@fst.rnu.tn adnen.Rajhi@esti.rnu.tn ali.gharsallah@fst.rnu.tn
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